The current thrust of our studies of neonatal drug metabolism lie in the area of transplacental carcinogenesis. The model used is the administration late in pregnancy of 3-methylcholanthrene to pregnant mice. It is known that the offspring of such animals have a high incidence of tumors during late adulthood. We plan to evaluate mixed-function oxidase activity in various organs during different developmental stages of such animals. Also studied will be the response of these animals to inducers such as phenobarbital and 3-methylcholanthrene. Another phase of our studies will be to examine the effect of exposure of rats to intense blue light on microsomal drug metabolism in liver and skin. These studies are designed to evaluate possible responses to high intensity light such as those encountered during the clinical practice of phototherapy of jaundiced infants. Other projects include a study of the possible inhibitory effect of progesterone and related steroids on the induction of hepatic drug metabolizing enzyme activity and a pursuance of our studies of the pharmacokinetics of digoxin.